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First post! I have a 1992 S10 Blazer 4.3 vortec 4X4 CPI. Interesting problem just poped up on me while I was driving around. My blazer stalled out on me when I pulled up to a stop light. Not being to worried about it, I restarted it with no problem and went on my way. Got to the next stopping point and the same thing happened again. One way that I found to help this problem was to put the truck in neutral before I came to a complete stop. Soon enough even that didn't work. I swapped out the IAC valve and thought that it fixed the problem but didn't. After the vehicle warmed up, it will stall out unless you keep giving it some gas. Took it to my brother-in-laws and hooked it up to his scanner to check it out. There is an O2 code present. We were able to see that the IAC was working properly. The truck would idle fine at first while cold, but when warm it would stall out as soon as we tried to put it in gear. After 10 minutes of playing with it it also decided to start stalling out in neutral also. FYI, After it stalls out, it starts up again with no problem what so ever. Any ideas???

No I didn't. I don't think that it is a fuel delivery issue. There is a new fuel pump, filter, and CPI on this vehicle. all have been replaced within the last 2 years. It has only been driven about 5k in that time period. When it stells out, there is no sputter at all. And it starts right back up with no problem at all. As I was driving it home a coyuple of days ago, I noticed it starting to surge a little bit going down the road at about 55 mph. Really wierd.

When my engine did that to me, it turned out the distributor timing/orientation was not aligned correctly.
But it could also be a cracked distributor cap or something else that prevents the engine from firing in the right moments.
A faulty spark plug?
Incorrect timing is often less of a problem at higher rotations, but at idle speed it may just choke the engine.
If I am not mistaken the idle speed of the engine is slower when it is in gear, so the reason why it shuts of when you put it in "Drive" might just be the slower engine speed in combination with misaligned timing.

Other possibility would be that the fuel/gas for idle it set too low.

But I don't know how these problems could just appear. In my case it was because I hadn't put things together in exactly the right way after a repair job (aligned the distributor by ear instead of using a timing light).

I would check out the injector wiring harness that runs into the intake manifold (exits just under the throttle body) before jumping to the conclusion that the ECU is the problem. They have been known to cause strange problems and are most often overlooked.

Just checked the fuel pressure. It looks as though it is a little low (around 52 psi when on). But it holds the pressure well. It doesn't leak down hardly at all. Went down about 10 psi in an hour. Please let me know if that is normal. I also just replaced the TPS and the same thing happens. It will start up perfectly,run for about 15 minutes, then stall out when it starts to get warm. When you restart it, it starts with no problem, but stalls out after about 10 seconds. Let me know what you think.